ATP-sensitive K ⁺ -channel run-down is Mg ²⁺ dependent

Abstract

ATP-sensitive K + -channel currents were recorded from isolated mem­brane patches and voltage-clamped CRI-G1 insulin-secreting cells. Inter­nal Mg 2+ ions inhibited ATP-K + channels by a voltage-dependent block of the channel current and decrease of open-state probability. The run­ down of ATP-K + channel activity was also shown to be [Mg 2+ ] i depen­dent, being almost abolished in Mg 2+ -free conditions. Substitution of Mn 2+ for Mg 2+ did not prevent run-down, nor did the presence of phos­phate-donating nucleotides, a protease or phosphatase inhibitor or replacement of Cl by gluconate.

Mg2+‐dependent inhibition of KATP by sulphonylureas in CRI‐G1 insulin‐secreting cells

“…The principle reasons for this are the wide variations in the channel activity between patches and the phenomenon of channel run-down which occurs in the presence of Mg2" (Kozlowski & Ashford, 1990). In order to obtain reliable data therefore, it is necessary to use relatively high drug concentrations as exemplified by the present study.…”

“…Outward current (defined as the current flowing from the intra-to the extracellular side of the membrane) is shown as upward deflections on all traces. The single channel current analysis was determined off-line using a programme that incorporated a 50% threshold crossing parameter to detect events (Dempster, 1988) (Kozlowski et al, 1989;Kozlowski & Ashford, 1990 were applied at 2 s intervals as described previously (Sturgess et al, 1988;Kozlowski et al, 1989 In experiments using the inside-out configuration, the pi- …”

“…For example, this divalent cation is at least partially responsible for the inward rectification displayed by this ion channel (Findlay, 1987;Ciani & Ribalet, 1988). In addition, Mg2" has a direct inhibitory effect upon the open state probability of the channel (Findlay, 1987;Ashcroft & Kakei, 1989) and is critically involved in the process of rundown (Kozlowski & Ashford, 1990), since complete removal of this cation from the intracellular compartment drastically reduces the rate of loss of channel activity with respect to time. The presence of intracellular Mg2" also influences many of the interactions between nucleotides and KATP.…”

Diazoxide‐sensitivity of the adenosine 5′‐triphosphate‐dependent K+ channel in mouse pancreatic β‐cells

“…(3) The Mg complex of ATP (MgATP) prevents or slows considerably the rapid decline in channel activity (channel run-down) observed in inside-out membrane patches in the absence of MgATP (Ohno-Shosaku et al, 1987); MgATP might act by serving as substrate for one or several protein kinases closely associated with the P-cell plasma membrane. However, run-down of K-ATP-channel activity was almost abolished in Mg2"-free cytosol-like solution (Kozlowski & Ashford, 1990).…”

Amantadine and sparteine inhibit ATP‐regulated K‐currents in the insulin‐secreting β‐cell line, HIT‐T15

“…Ashcroft & Kakei, 1989;Niki et al, 1989). More recently, it has been reported that Mg-free solutions abolish rundown of K-ATP channel activity in CRI-Gi fl-cells (Kozlowski & Ashford, 1990). In later experiments, therefore, the bath contained (solution D, mM): KCI 140, CaCl2 4.6, EDTA 10 (about 30nM free Ca2+ and 1 nm free Mg2+), HEPES 10 (pH 7.2 with KOH).…”